1. Field of the Invention
The present invention relates to a method of grinding the rear surface of a wafer to form a concavity therein and an unevenness absorbing pad for supporting a wafer during its grinding.
2. Related Art
A wafer having a plurality of IC, LSI or like devices formed on its front surface is cut into the individual devices by means of e.g. a dicing apparatus and those devices are widely used in various kinds of electronic machines and instruments. Before a wafer is cut into the individual devices, it is ground on its whole rear surface, while its front surface is held by a chuck table in a grinding machine, so that its thickness may be reduced to, say, 20 to 100 μm to enable a reduction in size and weight of electronic machines and instruments, as described in, for example, JP-A-2004-319885.
However, a wafer ground and reduced in thickness loses rigidity and its handling and transportation are thereafter difficult. For example, its handling is not easy when it has to be removed from the chuck table in the grinding machine, or when it has to be cut into the individual devices, and it is also difficult to transport from one process step to another. Its handling is also difficult when its ground rear surface has to be coated with a gold, silver, titanium or other metal film having a thickness of several tens of nanometers, and its electrical testing is also difficult.
Moreover, a wafer having a very small thickness not exceeding 50 μm gives devices having uneven rear surface with a low degree of flatness having protrusions and depressions matching those of the front surface, and those devices have undesirably low die strength.